Why/when I would need to use these flags in other cases?

Could regular Qt-based code still use the Qt built like this?

Why, in this case, the particular names "QtCppIntegration" and "CppIntegration"?

qtnamespace compiles Qt into a namespace and qtlibinfix modifies the names of the Qt dlls. For example: qtlibinfix renames all the Qt dlls with the infix you have chosen, for example to QtGuiCppIntegration.dll and qtnamespace wraps all of the Qt code in the namespace QtCppIntegration

Yes

The reason there is a difference between the naming of the options "QtGuiCppIntegration" and "CppIntegration" is simply that if qtlibinfix had the option "QtCppIntegration then the resulting dll names would be e.g "QtGuiQtCppIntegration" which does not look as nice as QtGuiCppIntegration

You said that code that was written for normal Qt can be used with Qt built like this, but I assume that some changes must be made to some makefile /.pro file... Correct? If so, is there a simple example somewhere?

Does anyone know why the Eclipse integration needed these flags?

For the Eclipse integration, was the choice of "CppIntegration" arbitrary, or was that exact name needed to integrate with some other library?